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Old 5th June 2005, 04:28 PM   #1
ash_dac is offline ash_dac  United Kingdom
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Default Arcam Alpha- fuse keeps blowing

Hi,


I purchased an original Arcam Alpha( untested ), and replaced the mains cable connections.

The secondary transformer connections had been re-done (looked like the connections had broke in the past, and had been resoldered with paper clips). Anyway, I sorted the connections out but the fuse still blows on turn on.

I've taken out the transfomer, and tested that the coils conduct electricity. Any more tests i can perform on it?

In terms of fixing the thing I have only got these ideas?


1. Output stage fried (driving into a short)
2. Transformer dead?
3. Short somewhere on PCB
4. PSU capacitors have failed

any more?

To detail the problem again:-It is meant to have a 500ma fuse in there, even tried a 2A one and that went pop. The fuse is connected to the primary transformer core.

If i can't fix it I will harvest the bits



Kind regards,


Ashley.
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Old 5th June 2005, 04:43 PM   #2
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Ashley,

What resistance do you measure across the primary, across the secondaries and between primary and secondary. Have you checked that the board is linked for 240V mains ?

Jon
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Old 5th June 2005, 06:34 PM   #3
Bare is offline Bare  Canada
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Dunno how much relevance this is, but my d290 had similar problem the other day..
One of the rectifier Diodes in the power supply failed..
seems someone at the Factory installed an errr.. incorrect one.. Did last 10 years despite that though
Lift them and Meter them.. might be an Easy fix.
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Old 5th June 2005, 07:28 PM   #4
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Ashley,

For the UK, FS201 should be fitted (FS202 should not, this is for 115v). FS201 should be 1.25Amps I believe. If you disconnect the secondaries of the transormer from the amp and power it up does the fuse still blow ?

Regards,

Jon
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Old 5th June 2005, 07:49 PM   #5
ash_dac is offline ash_dac  United Kingdom
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Jon,


Thanks for the information.

Inside it says 100-120V: 1.25A (T) ,and 220-240V: 500mA (T)

The secondaries were wired up for 240V according to the PCB notes.

On the back of the unit 240V is not painted over, below it says 120VA max.


Kind regards.


Ashley.
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Old 5th June 2005, 07:51 PM   #6
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Ashley,

Which model Alpha do you have? My notes obviously don't match your amp!

Jon
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Old 5th June 2005, 09:02 PM   #7
ash_dac is offline ash_dac  United Kingdom
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Jon,

It just says Arcam Alpha. 1984 on PCB.


Kind regards,


Ashley.
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Old 5th June 2005, 09:15 PM   #8
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Ashley,

If it just says Arcam Alpha on the front of the amp then I assume it must be the original Alpha instead of the later Alpha 5/6/7/8/9/1 ?

Try and measure the resistance of the transformer as I previously described. Also let me know what happens if you disconnect the secondary of the transformer from the rest of the amp and power it up. This will enable you to isolate the problem between the mains input and the transformer.

Jon
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Old 6th June 2005, 09:10 PM   #9
ash_dac is offline ash_dac  United Kingdom
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Jon,


Disconnected the secondary: still blows fuse!

I don't have a multimeter (brother destroyed his last week) so I had to improvise using a 5V dc 500mA supply . The primary core can be wired for both 240/120V.

Thes are the details on the pcb:-

black BRN+Red Orange 240V

Black+Red Brwn+Orange 110V/120V


Upon testing (note with a 5V dc 500mA power supply for safety) all primary wires seemed to conduct electricty with each other. I don't think this is right. I thought there were two 110V primary's that would connect to make a 240V combined primary.


Kind regards,


Ashley.

Note:- Fiddling with a PSU is potentially dangerous.If in doubt seek a qualified electriction for guidance.
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Old 6th June 2005, 10:49 PM   #10
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Ashley,

>Disconnected the secondary: still blows fuse!

This is positive, at least you've isolated the problem !

>Upon testing (note with a 5V dc 500mA power supply for safety) all primary wires seemed to conduct electricty with each other. I don't think this is right.

True if the transformer has twin primaries, connected in series for 240v and parallel for 120v but if it has a centre tapped primary (centre for the 120V) then they *would* all be connected.

If you have a dc supply then why not connnect it across the primary side and connect a bulb (with current limiting resistor) between the 0V of the supply and each wire of the secondary. This will tell you if the primary and secondary are shorted - since DC should not flow across the transformer.

You'll find this much easier with a multimeter !!

Jon
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